The invention is related to a probe for a scanning type microscope which images a surface structure of a specimen, wherein nanotubes such as a carbon nanotube, BCN (boron carbon nitride) series nanotube, BN (boron nitride) series nanotube, etc. are used for the probe needle, in more detail, related to a probe for a scanning type microscope produced by focused ion beam machining which is manufactured by means of processes such as the nanotube of fastening, purifying and cutting using a focused ion beam apparatus.
In order to image a surface structure of a specimen by an atomic force microscope abbreviated as AFM, a scanning needle is needed which is caused to approach to the surface of the specimen for getting information from it. As the scanning needle, a cantilever made of silicon or silicon-nitride, on the tip of which a protruding portion (or pyramid portion) is formed, has been known in the past.
A conventional cantilever is formed by means of the micro-fabrication technique such as lithography, etching, etc. Since the cantilever detects atomic force from the surface of specimen by the tip of protruding portion, the degree of cleanness of an image is determined by the degree of sharpness of the tip portion. Then, in the sharpening treatment of the tip end of the protruding portion serving as a probe needle, an oxide process and an etching process for an oxide film which are sort of semi-conductor process technique are utilized. However, there is a lower limit in a reduction of size even in the semi-conductor process technique, so that the degree of sharpness of the tip end of the protruding portion described above is also physically limited.
On the other hand, a carbon nanotube was discovered as a carbon matter having a new structure. The carbon nanotube is from about 1 nm to several 10 nm in diameter and several xcexcm in length, and its aspect ratio is around 100xcx9c1000. It is difficult to form a probe needle of 1 nm diameter by means of the present technique of semiconductor. Therefore, in this respect, the carbon nanotube provides best condition for the probe needle of an AFM.
In such a situation, H. Dai and others published, in Nature (Vol.384, Nov. 14, 1996), a report with respect to an AMF probe in which a carbon nanotube is stuck on the tip of the protruding portion of a cantilever. Though the probe proposed by them was of epoch-making, the carbon nanotube fell off from the protruding portion during repeatedly scanning surfaces of specimens, since the carbon nanotube was simply stuck on the protruding portion
In order to solve this weak point, the present inventors have achieved to develop a method fastening firmly the carbon nanotube to the protruding portion of the cantilever. Results of this invention have been published as the Japanese patent application laid-open (Kokai) Nos. 2000-227435 and 2000-249712.
The first fastening method above-mentioned is that a coating film is formed in an electron microscope by irradiating an electron beam to the base end portion of a nanotube, and next the nanotube is fastened to the cantilever by means of covering the nanotube with the coating film. The second method is that the base end portion of the nanotube is fusion-fastened to the protruding portion of the cantilever by irradiating an electron beam on the base end portion of the nanotube or by causing to flow current, in an electron microscope.
It is a quite skilful method to fasten by coating or fusion-welding a nanotube base end portion using an electron beam, while enlarging an object image by means of an electron microscope. However, there is a limit in energy intensity of an electron beam of the electron microscope, so that this fact causes to yield a limit for coating-strength or fusion-welding-strength, and as the result, it was difficult to obtain fastening-strength beyond a certain degree.
Besides, lengths of nanotubes produced by an arc-discharge are inhomogeneous, so that it is necessary finally to homogenize quality of the nanotube products by unifying the lengths of the nanotubes. However, due to the above limit in the electron microscope, the cutting process of the nanotube has difficult points, so that the control of the nanotube length was not enough well done.
Furthermore, since an electron microscope is a device for treating electron beams, though it is possible to irradiate an electron beam, but being impossible to diffuse atoms of another element, or to implant ions into a probe needle nanotube, therefore, the improvement of the quality of nanotubes has not been progressed
The essential aim of the electron microscope is to obtain enlarged images of specimens in a clean imaging room being in the vacuum state. However, when an organic gas flows into this electron microscope and decomposes, a body-tube and the imaging room, which should be clean, are polluted with the organic gas or the decomposed matter. If this pollution gas is absorbed in and re-emitted from a wall-surface, the gas adheres to a surface of a cantilever. But, since it is difficult to remove the adhered pollution matter by an electron beam, this fact shows that there is a technical limit of the electron microscope, in manufacture of the nanotube probe needle.
Accordingly, an object of the present invention is to find an apparatus other than the electron microscope as a device in which the nanotube is fastened to a protruding portion of a cantilever, and to provide a probe for a scanning type microscope which can fasten and cut a nanotube probe needle and furthermore can improve the quality of the nanotube probe needle by implanting another element atoms, etc.
The present invention provides, in a probe for a scanning type microscope, by which substance information of a specimen is obtained by means of a tip end of a nanotube probe needle fastened to a cantilever; a probe for a scanning type microscope produced by focused ion beam machining, which is characterized in that the nanotube is fastened to a cantilever with a decomposed deposit produced by decomposing an organic gas by means of a focused ion beam in a focused ion beam apparatus.
The present invention provides a probe for a scanning type microscope described in the first part of the present invention, wherein a hydrocarbon is used for the above described organic gas.
The present invention provides a probe for a scanning type microscope described in the first part of the present invention, wherein an organic-metallic gas is used for the above described organic gas.
The present invention provides a probe for a scanning type microscope described in the first part of the present invention, wherein a silicon cantilever, a silicon-nitride cantilever or a cantilever coated with a conductive substance are utilized as the above described cantilever.
The present invention provides a probe for the scanning microscope produced by focused ion beam machining which is characterized in that unnecessary matter existing in a predetermined region is removed by irradiating an ion beam to the predetermined region of a nanotube probe needle fastened to the cantilever.
The present invention provides a probe for a scanning type microscope described in the fifth part of the present invention, wherein the above described unnecessary matter is a unnecessary deposit heaping up at a tip end portion of the nanotube probe needle or a unnecessary deposit heaping up near a base end portion of the nanotube.
The present invention provides a probe for the scanning microscope produced by focused ion beam machining which is characterized in that an unnecessary part of the nanotube probe needle is cut off and the length of tip end portion of the nanotube probe needle is controlled by irradiating an ion beam to the tip end portion of the nanotube probe needle fastened to the cantilever.
The present invention provides a probe for a scanning type microscope described in the seventh part of the present invention, wherein the nanotube is cut in a perpendicular or an oblique direction, in the cutting of the unnecessary part above described.
The present invention provides a probe for the scanning microscope produced by focused ion beam machining which is characterized by changing physical and chemical qualities of the probe needle by irradiating an ion beam to the predetermined region of the tip end portion of the nanotube probe needle fastened to the cantilever.
The present invention provides a probe for a scanning type microscope described in the ninth part of the present invention, wherein the above described ion element is fluorine, boron, gallium, or phosphorus.
The present inventors had earnestly investigated a device being substituted for an electron microscope, and as the result, had gotten an idea to use an ion beam instead of an electron beam; specifically had achieved an idea to utilize a focused ion beam apparatus (abbreviated as FIB apparatus) which can focus at will the ion beam and can process an object.
This FIB apparatus is a device by which various atoms are ionized, the ions are accelerated by means of an applied electric field, and this ion beam is focused by means of an electric field lens so that the beam section is made fine and the beam comes to be a high energy state, and by which a target is processed by means of irradiating the resultant focused ion beam to the target. Accordingly, the FIB apparatus comprises partial devices such as an ion source, an acceleration apparatus, a beam-focusing apparatus and a beam-operating device, etc.
An applied voltage can be freely arranged, and the energy of the ion beam can be arbitrarily set up by the acceleration apparatus. Various processes for nanotubes are possible by means of arrangement of the energy of the ion beam. By the present invention, an organic gas which is induced into a reaction chamber of the FIB apparatus is decomposed by the ion beam. Leaving a nanotube base end portion adhered to a protruding portion of a cantilever disposed in the reaction chamber, the above described decomposed gas heaps up on this base end portion, so that the nanotube is strongly fastened to the protruding portion of the cantilever by this decomposed deposit. In this manner, the xcx9c related to the present invention is accomplished.
In a case where the organic gas is a hydrocarbon gas, the above described decomposed deposit is a carbon deposit, and the nanotube is fastened to the protruding portion by means of this carbon deposit. In a case where the organic gas is an organic-metallic gas, the above described decomposed deposit is a metallic deposit, and the nanotube is fastened in a conductive state to the protruding portion by means of this metallic deposit.
As substances of the above-described hydrocarbon series, there are hydrocarbons of methane series, hydrocarbons of ethylene series, hydrocarbons of acetylene series, cyclic hydrocarbons, etc.; more concretely saying, hydrocarbons of less molecular-weight such as ethylene or acetylene are favorable among them. Furthermore, as the above-described organic-metallic gases, the following gases can be utilized; for examples, W(CO)6, Cu(hfac)2, (hfac: hexa-flouro-acetyl-acetonate), (CH3)2AlH, Al(CH2xe2x80x94CH)(CH3)2, [(CH3)3Al]2, (C2H5)3Al, (CH3)3Al, (Ixe2x80x94C4H9)3Al, (CH3)3AlCH3, Ni(CO)4, Fe(CO)4, Cr[C6H5(CH3)2], Mo(CO)6, Pb(C2H5)4, Pb(C5H7O2)2, (C2H5)3PbOCH2C(CH3)2, (CH3)4Sn, (C2H5)4Sn, Nb(OC2H5)5, Ti(i-OC3H7)4, Zr(C11H19O2)4, La(C11H19O2)3, Sr[Ta(OC2H5)6]2, Sr[Ta(OC2H5)5(Oc2H4OcH3)]2, Ba(C11H19O2)2, (Ba,Sr)3(C11H19O2), Pb(C11H19O2)2, Zr(OtC4H9)4, Zr(OiC3H7)(C11H19O2)3, Ti(OiC3H7)2(C11H19O2), Bi(OtC5H11)3, Ta(OC2H5)5, Ta(OiC3H7)5, Nb(OiC3Hxe2x80x2)5, Ge(OC2H5)4, Y(C11H19O2)3, Ru(C11H19O2)3, Ru(C5H4C2H5)2, Ir(C5H4C2H5)(C8H12), Pt(C5H4C2H5)(CH3)3, Ti[N(CH3)2]4, Ti[N(C2H5)2]4, As(OC2H5)3, B(OC2H3)3, Ca(OCH3)2, Ce(OCxe2x80x3H5)3, Co(OiC3H7)2, Dy(OiC3H7)2, Er(OiC3H7)2, Eu(OiC3H7)2, Fe(OCH3)3, Ga(OCH3)3, Gd(OiC3H7)3, Hf(OCH3)4, In(OCH3)3, KOCH3, LiOCH3, Mg(OCH3)2, Mn(OiC3H7)2, NaOCH3, Nd(OiC3H7)3, Po(OCH3)3, Pr(OiC3H7)3, Sb(OCH3)3, Sc(OiC3H7)3, Si(OC2H5)4, VO(OCH3)3, Yb(OiC3H7)3, Zn(OCH3)2, etc.
As for the nanotube, there are a conductive carbon nanotube or an insulation nanotube of BN series and of BCN series. And as for the cantilever for an AFM, there are a semi-conduction silicon cantilever and an insulation silicon-nitride cantilever. But a conductive cantilever can be manufactured by coating on a cantilever surface including the protruding portion with a conductive film such as metal, etc. and in the similar manner, the insulation nanotube can be transmuted to a conductive nanotube.
Accordingly, a conductive probe for an ion type scanning type microscope can be manufactured by means of electrically connection of the conductive nanotube with the conductive cantilever using a conductive deposit such as a metallic deposit. The conductive probe, owing to its conductivity, can be utilized not only for the AFM but also for a STM (tunneling microscope) which detects a tunnel-current. However, if the semi-conduction cantilever or the insulation cantilever is used as a cantilever, the cantilever, due to non-conductivity, can be used as the probe for an ordinary AFM which detects flexion.
As for the probe for the scanning type microscope related to the present invention, there are not only the above-described AFM and STM, but also a level force microscope (LFM) which detects differences of a surface by means of friction force, a magnetic force microscope (MFM) which detects magnetic interaction, an electric-field force microscope (EFM) which detects a gradient of an electric field, and a chemical force microscope (CFM) which images surface distribution of a chemical function group. All such microscopes are for obtaining surface information of specimens at the atomic level.
The tip end of a nanotube is a probe needle for detection. If an unnecessary deposit adheres to the tip end of the nanotube, this portion works as a probe needle so that the tip end of the nanotube captures error information and the image is caused to be dim. Accordingly, the unnecessary deposit adhering to the nanotube tip end portion is removed by means of ion beam irradiation, by increasing the ion beam energy of the FIB apparatus higher.
As was described above, in the present invention, the tip end portion of the nanotube is fastened to the protruding portion of the cantilever by means of the decomposed deposit. In a case where this decomposed deposit is formed to expand up to an unnecessary region, second processes such as a formation of a conductive film, etc. are caused to be difficult. In such a case, this unnecessary decomposed deposit near the base end portion can be removed by means of irradiation of a focused ion beam.
Length of produced nanotubes is in general quite indefinite. However, in order to unify nanotube quality, it is necessary to make uniform the lengths of the nanotube tip ends. Then, by solution-cutting the unnecessary parts of the nanotubes by means of the ion beam, the length of the nanotube is controlled. For this purpose, the energy of the ion beam is increased or an irradiation period is arranged.
In addition, in order to improve a quality of the nanotube tip end, ions can be shot into the nanotube by the FIB apparatus. Ions accelerated in high energy can be shot into the inner space of the nanotube, but low energy ions is driven on a surface layer of the nanotube and coats the surface of the nanotube. Particularly, when ions are shot into the tip end of the nanotube probe needle, these ions directly act to a surface of a specimen.
As the sort of the ion, an arbitrary element can be chosen, for examples, such as fluorine, boron, gallium, or phosphorus, etc. These atoms react on a carbon atom in the nanotube to form CF-combination, CB-combination, CGa-combination or CP-combination, which come to possess specific properties for these combinations.
In a case where the ions shot into the tip end of the nanotube are ferromagnetic atoms such as Fe, Co, Ni, etc., this probe for a scanning type microscope can be utilized for an MFM. That is, since these ferromagnetic atoms detect ferromagnetism of a surface of a specimen at the atomic level, this technique can greatly contribute to the progress of substance engineering such as the resolution of magnetic structure of a sample substance, etc.